Fire and heat resistant laminating resins based on maleimido and citraconimido substituted 1-[(diorganooxyphosphonyl)methyl]-2,4- and -2,6-diaminobenzenes

ABSTRACT

The subject invention pertains to a novel class of fire- and heat-resistant bisimide resins prepared by thermal polymerization of maleimido or citraconimido substituted 1-[(dialkoxyphosphonyl)methyl]-2-4 and -2,6-diaminobenzenes. Typical polymer precursors have the chemical structure: ##STR1## wherein R is alkyl, substituted alkyl or aryl, and R 1  is hydrogen or lower alkyl. 
     The polymer precursors are prepared by reacting 1-[(diorganooxyphosphonyl)methyl]-2-4- and -2,6-diaminobenzenes with maleic anhydride or citraconic anhydride in a mole ratio 1:2. Chain extension of the monomers is achieved by reacting the mono-N-maleimido derivatives of 1-[(diorganooxyphosphonyl)methyl]-2,4 and -2,6-diaminobenzenes with aryl tetracarboxylic dianhydrides, such as benzophenone tetracarboxylic dianhydride, or aryl diisocyanates, such as methylenebis(4-phenylisocyanate), in a mole ratio 2:1. The polymerization of the monomers is studied by differential scanning calorimetry (DSC) and the thermal stability of the polymers is ascertained by thermogravimetric analysis (TGA).

ORIGIN OF THE INVENTION

The invention described herein was made in the performance of work undera NASA contract and is subject to the provisions of Section 305 of theNational Aeronautics and Space Act of 1958; Public Law 85-568 (72 Stat.435; 42 U.S.C 2457).

BACKGROUND OF THE INVENTION

Related Applications

This application is a continuation-in-part of our copending applicationSer. No. 522,629, filed Aug. 12, 1983 now abandoned, which is directedto compounds and polymers having ##STR2## repeating units, and isincorporated herein by reference. This application is also related tothe following commonly assigned patent applications: U.S. Ser. No.641,152, filed Aug. 16, 1984, which is directed to the above compoundsand polymers; U.S. Ser. No. 641,142, filed Aug. 16, 1984, which isdirected to the above mentioned compounds and polymers; U.S. Ser. No.641,153 filed Aug. 16, 1984, which is directed to polyimides andcopolyimides prepared from the present diaminobenzenes; and U.S. Ser.No. 641,143, now U.S. Pat. No. 4,536,565, filed Aug. 16, 1984, which isdirected to polyimides and copolyimides from the presentdiaminobenzenes, all of which are pending.

FIELD OF THE INVENTION

The invention relates to fire- and heat-resistant bisimide resinsobtained by thermal polymerization of maleimido or citraconimidoderivatives of 1-[(diorganooxyphosphonyl)methyl]-2,4- and-2,6-diaminobenzenes.

DESCRIPTION OF THE ART

High temperature resistant polymers are used extensively in advancedaerospace structures in which structural integrity must be retainedduring continuous use at temperatures of 325° C. and above. Thestringent requirements of space technology and of other industrialapplications for thermal protective materials have led to thedevelopment of several classes of heat- and fire-resistant heterocyclicpolymers. Aromatic polyimides have met these requirements to a largeextent and are obtained by condensation reactions. However, the loss ofdesirable mechanical properties and problems of reproducibility havebeen observed because of the voids created by the elimination of wateror difficulty in the removal of the high-boiling-point solvent or both.As a result, the use of these polyimides as laminating resins or foradhesives has been limited.

Initial attempts to overcome these processability problems led to thedevelopment of addition polyimides based on short, preimidized segmentswhich polymerize thermally through end groups without loss of volatiles.However, these polymers were found to be inherently brittle because ofthe extensive crosslinking which occurs during polymerization. Severalamine-capped liquid elastomeric prepolymers reacted with bismaleimidesto produce polymers. See for example, P. Kovacic, U.S. Pat. No.2,818,405; Chem. Abstracts, 52, 5018e (1958). However, these polymerscould not be considered heat-resistant.

Several investigations concerning flame retardation of polymide resinsprepared from phosphorous-containing prepolymers, end-capped withreactive maleimido rings, have been recently reported. Bisimide resinsbased on bis(m-aminophenyl)methylphosphine oxide as well as bisimide andtriimide resins based on tris(m-aminophenyl)phosphine oxide have beenprepared and tested as a matrix for fiber-reinforced composites. See,for example, U.S. Pat. No. 4,276,344 and I. K. Varma, G. M. Fohlen andJ. A. Parker, J. Macromol. Sci-Chem, (1), 39 ff (1983). Some of thepolymer precursors show a relatively high curing temperature or yieldinherently brittle polymers due to their high cross-linking density. Itis desirable to have organic matrix resins with a low curing temperatureso as to obtain polymers with reduced brittleness.

Some patents of general interest in this field include the followingU.S. Pat. Nos: 3,929,713; 4,269,961; 4,107,153; 4,276,344; 4,283,522;and 4,421,820.

Some references of the inventors, which describe fire resistantcompositions of phosphorus-containing polymers and the monomers thereof,include the following:

1. J. A. Mikroyannidis and D. A. Kourtides, "Fire-Resistant Compositionsof Epoxy Resins with Phosphorus Compounds", Symposium on Rubber-ModifiedThermoset Resins, 186th Annual American Chemical Society Meeting,Washington, D.C., Abstract PMSE 133, Aug. 28-Sept. 2, 1983; 2. J. A.Mikroyannidis and D. A. Kourtides, "Fire-Resistant Epoxy ResinsContaining 1-(Di(2-Chloroethoxy phosphinyl) Methyl)-2,4- and 2,6Diaminobenzene as Curing Agent", Proceedings of the 12th North AmericanThermal Analysis Society Conference, Williamsburg,Va (Sept. 1983);

3. J. A. Mikroyannidis and D. A. Kourtides, "Curing of Epoxy Resins with1-[Di(2-Chloroethoxyphosphinyl)Methyl]-2,4- and 2,6-Diaminobenzene",Journal of Applied Polymer Science, Vol. 29, pp. 197-209, (1984);

4. J. A. Mikroyannidis and D. A. Kourtides, "Curing of Epoxy Resins with1-[Di(2-Chloroethoxyphosphinyl)Methyl]-2,4- and 2,6-Diaminobenzene",National Aeronautics and Space Administration Report No. TM 84350, Oct.1983;

5. J. A. Mikroyannidis and D. A. Kourtides, "Synthesis andCharacterization of Phosphorus-Containing Polyamides and Copolyamidesbased on 1-[Dialkoxyphosphinyl)Methyl]-2,4- and -2,6-Diaminobenzenes",Journal of Applied Polymer Science, Vol. 29, pp. 941-953 (1984);

6. J. A. Mikroyannidis and D. A. Kourtides, "Synthesis andCharacterization of Phosphorus Containing Polyamides and CopolyamidesBased on 1-[(Dialkoxyphosphinyl) Methyl]-2,4- and -2,6-Diaminobenzenes",Proceedings of the Society for the Advancement of Materials and ProcessEngineering, Reno, Nev. (Apr. 1984); and

7. J. A. Mikroyannidis and D. A. Kourtides,"Curing of Epoxy Resins with1-[Di(2-Chloroethoxyphosphinyl)Methyl]-2,4- and -2,6-Diaminobenzene",Proceedings of the Society of Plastics Industry Annual Spring Meeting,St. Louis, Mo. (May 1984).

These references of the inventors are not considered to be prior artconcerning the present invention.

OBJECTS OF THE INVENTION

It is an object of the present invention to provide novel phosphorous-or phosphorous and chlorine-containing maleimido and citraconimidoend-capped monomers which have a relatively low melting temperature andcan polymerize at moderate temperatures to produce rigid bisimide resinswithout elimination of volatiles or formation of voids.

It is a further object of the invention to provide polymer precursorssoluble in solvents such as methyl ethyl ketone (MEK), dimethyl ketone(acetone), and tetrahydrofuran (THF) which are very suitable and oftenreferred as "varnish" solvents for composite fabrication. Moreover,molten polymer precursors may be used as adhesives without utilization asolvent due to their low melting temperature and the higherpolymerization temperature.

It is a further object of the invention to provide bisimide resinsobtained by thermal polymerization of monomers which are improved withrespect to one or more of the properties limiting oxygen index (LOI),char yield and smoke evolution. They are useful for purposes such as,for example, lamination which combine good fire- and heat-resistancewith good mechanical properties, for composites and laminates for use inaircraft structures.

It is a further object of the invention to provide bisimide resins withreduced brittleness. For this purpose the formula weight and the lengthof the bridge between the two maleimido groups was increased byincorporation of benzophenone tetracarboxylic dianhydride ormethylenebis(4-phenylisocyanate) as a building unit of this bridge. Thechain extension of monomers is expected to reduce brittleness of thebisimide resins, since larger polymer segments would be available forinternal motions after crosslinking.

BRIEF DESCRIPTION OF THE DRAWING

The invention is further described with relevence being made to theaccompanying drawing wherein FIG. 1 is a graph illustrating the reducedsmoke evolution of some polymers which results from practicing thepresent invention.

BRIEF SUMMARY OF THE INVENTION

In accordance with the invention various polymer monomers or precursorsare based on maleimido or citraconimido substituted1-[(diorganooxyphosphonyl)methyl]-2,4- and -2,6-diaminobenzenes of theformula: ##STR3## wherein R is an organo group selected from alkyls,substituted alkyls and aryls; and R¹ is hydrogen or lower alkyl. Thesemonomers are thermally copolymerized with dianhydrides and diisocyanatesto produce fire- and heat-resistant polymers which are used aslaminating resins, without the elimination of volatiles or formation ofvoids. The polymers combine one or more properties of heat-resistancelow flammability, high char yield, low smoke evolution, reducedbrittleness and good mechanical properties.

DETAILED DESCRIPTION OF THE INVENTION

The starting material of the present invention is a mixture of1-[(diorganooxyphosphonyl)methyl]-2,4 and -2,6-diaminobenzenes 1.##STR4## This mixture is a consequence of the method of synthesis (SeeExamples 1 to 4 below) and the 2,4-diamino isomer predominates. It isunnecessary for purposes of the present invention to separate theisomers. Compounds 1, though a mixture, will referred to as a compoundhaving the chemical structure of the predominant 2,4-diamino isomer. Ris an alkyl, substituted alkyl or aryl group. Examples of R are methyl,ethyl, n- and iso-propyl, higher (e.g., C4 to C10) alkyl, haloalkyl,especially chloroalkyl such as 2-chloroethyl; and aromatic groups, suchas phenyl, substituted phenyl, naphthyl, e.g., tolyl, etc. Ethyl and2-chloroethyl groups are preferred, e.g., Compounds 1a and 1b. ##STR5##

The diamines 1 may be prepared as described in the related application(ARC-11425-2) referred to above. Briefly stated, a1-[(diorganooxyphosphonyl)methyl]benzene, (RO)₂ P(O)CH₂ C₆ H₅, isnitrated by a mixture of fuming nitric and sulfuric acid to thecorresponding dinitro derivatives which are then reduced by catalytichydrogenation to the diamino species 1.1-[(Diethoxyphosphonyl)methylbenzene and1-[(di-2-chloroethoxyphosphonyl)methyl]benzene, both of which are knowncompounds, are used as starting materials for preparing the diamines 1aand 1b respectively.

The subject invention pertains to the synthesis of N-maleimido orN-citraconimido derivatives of diamines 1, which may be thermallypolymerized. More particularly, the polymer precursors 2: ##STR6## where2a: R=CH₂ CH₃ ; R¹ =H

2b: R=CH₂ CH₂ Cl; R¹ =H

are synthesized by condensation of diamines 1 (1 mol) with an anhydride,such as maleic anhydride (2 mol), where R¹ is hydrogen. Intermediatebismaleamic acid is cyclodehydrated "in situ" with acetic anhydrideusing sodium acetate as catalyst in boiling acetone. (Examples 5 and 6).

Similarly, the polymer precursors 3 where Compound 3a (R=CH₂ CH₃ and R¹=CH₃) and Compound 3b (R=CH₂ CH₂ Cl and R¹ =CH₃) are synthesized bycondensation of diamines 1 with an anhydride of the formula ##STR7##where R¹ is alkyl having one to six carbon atoms, e.g., methyl, wherecitraconic anhydride is used (See Examples 7 and 8).

The above methods produce a diamine/anhydride combining about oneequivalent of diamine with about two equivalents of anhydride. That isto say, more than twice as much dianhydride per diamine on an equivalentbasis is required to obtain compounds 2, 2a, 2b, 3a and 3b and the like.

If a polymer precursor having a free amine is desired, then a diaminesuch as 1 and an anhydride are combined in about a 1:1 equivalent ratio.That is to say, 1-[(Diorganooxyphosphonyl)methyl] benzene maleimide ofthe formula: ##STR8## is thus produced, where R is an organo groupselected from alkyls, substituted alkyls and aryls; A is a --NH₂ or a##STR9## group and B is the other group; where R¹ is hydrogen or loweralkyl, and A and B are in the 2,4 or 2,6-positions (See Examples 11 and12). Preferred embodiments of these monomaleimides are those where R isethyl or 2-chloroethyl, and R¹ is hydrogen or methyl.

Chain extension of the phosphonyl group connecting the two maleimidogroups is accomplished by reaction with an aryl tetracarboxylicdianhydride ##STR10## where Ar is a tetravalent aromatic groupcontaining from 6 to 20 carbon atoms. Thus, Ar may be a substituted arylgroup, phenyl, naphthyl, phenanthryl, benzophenonyl and the like.Preferred embodiments of the present invention include benzophenonetetracarboxylic dianhydride and pyromellitic dianhydride. Chainextension also includes aryl, alkylene and arylalkylene diisocyanates ofthe formula OCN--R² --NCO, where R² is a disubstituted aryl, such asphenyl, naphthyl; alkylene such as ethylene, pentylene, hexylene; orarylalkylene, such as methylenebisphenyl and the like. Preferredembodiments of the present invention include 1,3-phenylene diisocyanate,methylene bis(4-phenyl isocyanate), 2,4-toluene diisocyanate and thelike.

The polymerization of the dianhydrides may be considered to be atwo-stage polycondensation method. The first stage of the condensationis carried out in a solvent. The formation of the bismaleimidic acid isexothermic and is carried out at ambient temperature or slightly above.Under these conditions the extent of cyclodehydration is negligible.

Dehydration, the second stage of the imidization process can be carriedout by thermal or chemical means. After removal of the solvent thethermal process involves heating the polymer at about 280° C. in avacuum for 2 hr. The chemical means includes azeotroping the water ofcyclization with benzene or refluxing in acetic anhydride with sodiumacetetate as catalyst. The completion of the cyclization is ensured byheating the polymers at about 200° C. in a vacuum oven for two hours(See Examples 5 and 9).

Specifically, in the first stage the polymer precursors 4: ##STR11##where 4a: R=CH₂ CH₃

4b: R=CH₂ CH₂ Cl

were synthesized by reacting diamines 1 with an equimolar amount ofmaleic anhydride to yield the corresponding maleimido acids. The latterreacted subsequently with benzophenone tetracarboxylic dianhydride in amole ratio 2:1 and finally was cyclodehydrated using acetic anhydrideand sodium acetate (Examples 9 and 10).

Overall the polymerization of dianhydride and Compound 2 may besummarized as is shown in the sequence below: ##STR12## where Ar and Rare defined hereinabove and x is a positive integer. An embodiment is"x" between 1 and 1000 and a preferred embodiment is "x" between 10 and100.

In an analogous manner, the polymer precursors 5: ##STR13## where 5a:R=CH₂ CH₃

5b: R=CH₂ CH₂ Cl

were synthesized by reacting an aryl diisocyanate, OCN-Ar-NCO such asmethylenebis(4-phenylisocyanate), with the mono-N-maleimides of diamines1 (Examples 11 and 12).

Overall the polymerization of diisocyanate and Compound 1 may besummarized as is shown in the sequence below having the bracketedrecurring unit: ##STR14## where R and R² are defined hereinabove. "y" isa positive integer. An embodiment of the present invention is "y"between 1 and 1000. A preferred embodiment is "y" between 10 and 100.

In all cases of polymer precursors the diamino moiety is shown as the2,4-diamino compound (which predominates) but it will be understood thatthe 2,6-diamino compound is also present.

Bisimide resins are prepared by thermal polymerization of the polymerprecursors. The polymerization behavior of the polymer precursors wasanalyzed and determined by differential scanning calorimetry (DSC) innitrogen atmosphere. The results are listed in Table 1. In this Table,T₁ is the temperature of first energy release (start of polymerization),T₂ is the temperature of exothermic peak position, and T₃ is thetemperature of termination of polymerization. m-Phenylenebismaleimide,which is a conventional polymer precursor, is shown in this table asExperiment Number 6.

The thermal polymerization of the polymer precursors is achieved byheating them into an air draft oven at 180° C. for about 20 min untilmolten and subsequently at 230° C. for 2 hr.

The thermal stability of the polymers is ascertained bythermogravimetric analysis (TGA) both in N₂ and air atmosphere. Theresults are shown in Table 2. The polymers obtained from the precursors2, 3, 4, 5 and 6 by the thermal process mentioned above are referred toby the numbers 2', 3', 4', 5' and 6' respectively. PDT is the polymerdecomposition temperature, PDT_(max) is the maximum polymerdecomposition temperature, and TCP is the temperature of completepyrolysis. As is seen from Table 2, char yield is substantially greaterwith the phosphorus-containing polymers of the present invention thanwith conventional polymer (Polymer 6').

Table 3 sets forth data demonstrating superior fire-resistance of somepolymers. In this Table, LOI is the limiting oxygen index determinedaccording to the ASTM D 2863-74 method. LOI value indicates resistanceto ignition. As is seen in Table 3 the LOI values of polymers of theinvention are substantially greater than that of comparable Polymer 6'.The smoke density is determined according to the test method describedby National Fire Protection Assoc., Bull. No. NFPA 258-T (1974). FIG. 1shows the smoke density (Ds) value of smoke evolved from some polymersunder flaming conditions (heat flux=3.3 W/cm²) as a function of theirradiation time. The smoke density value indicates the flammability. Aswill be seen from Table 3 as well as from FIG. 1, the polymers of thepresent invention show a substantially lower smoke density than theconventional polymer 6'.

The following examples will serve to illustrate the practice andadvantages of the invention, and are not to be construed as limiting thescope of the invention. Examples 1 to 4 illustrate the preparation ofdiamines l. Examples 5 to 12 illustrate the preparation of the polymerprecursors.

The structure of the polymer precursors is confirmed by elementalanalysis, proton nuclear magnetic resonance (¹ H-NMR) and infraredspectroscopy (IR) and by gas chromatography-mass spectroscopy (GCMS).Melting temperatures of most of the polymer precursors synthesized werenot recorded by the standard test methods because they did not show aclear melting point, probably due to the formation of crossbonds ongradual heating of these compounds.

EXAMPLE 1 1-[(Diethoxyphosphonyl)methyl]-2,4- and -2,6-dinitrobenzenes

1-[(Dithoxyphosphonyl)methyl]benzene (21.76 g, 95 mmol) was addeddropwise to a mixture of fuming nitric acid (16.3 g) and fumingsulphuric acid (54.30 g), containing 30% 20₃, at 55° C. The addition ofthe phosphonate lasted 1 hr and subsequently the mixture was heated atthe same temperature for another hour. The mixture was poured into 1liter of ice water and extracted with chloroform (300 ml). Thechloroform solution was washed with 5% NaHCO₃ solution and with water,dried (Na₂ SO₄) and concentrated to give a yellowish solid (24.16 g,80%, mp 78°-82° C.). Recrystallizations from ether-chloroform (10:1vol/vol) gave an analytical sample; mp 101°-104° C. The structure wasconfirmed by ¹ H-NMR and chemical analysis.

EXAMPLE 2 1-[(Diethoxyphosphonyl)methyl]-2,4- and -2,6-diaminobenzenes,1a

The recrystallized product of Example 1 (2.00 g, 6.28 mmol) wasdissolved in 50 ml of absolute ethanol and a small amount of catalyst,10% palladium on carbon, was added. The hydrogenation was carried out ona Parr apparatus under a pressure of 3.5 atm at room temperature untilno more hydrogen was taken up (about 3 hrs.). After the filtration ofthe catalyst and the removal of the volatile components under vacuum aviscous undistillable liquid was obtained (1.57 g. 97%), which could notbe induced to crystallize. The dihydrochloride salt was formed bypassing anhydrous hydrochloride gas through its solution in chloroform.This salt was a nearly white solid and after recrystallizations fromethanol-ether (1:6 vol/vol) an analytical sample was obtained which wasdecomposed at temperature higher than 128° C. Structure was confirmed by¹ H-NMR and chemical analysis.

EXAMPLE 3 1-[(Di-2-chloroethoxyphosphonyl)methyl]-2,4- and-2,6-dinitrobenzenes

1-[(Di-2-chloroethoxyphosphonyl)methyl]benzene (5.13 g, 17 mmol) wasadded dropwise to a mixture of fuming nitric acid (4.0 g) and fumingsulphuric acid (13.0 g), containing 30% SO₃ at 55° C. The addition ofthe phosphonate lasted 0.5 hour and subsequently the mixture was heatedat the same temperature for 4 hours longer. The mixture was poured into300 ml of ice water and extracted with chloroform (150 ml). Thechloroform solution was washed with 5% sodium bicarbonate solution andwith water, dried (sodium sulfate) and concentrated to give a viscousliquid (4.92 g) diluted with about 100 ml of acetone-ether (1:10vol/vol). Upon cooling of the solution the title product wascrystallized (2.80 g, 42%, mp 79°-84° C.). Recrystallizations fromacetone-ether (1:10 vol/vol) gave an analytical sample: mp 83°-85° C.Structure was confirmed by ¹ H-NMR and chemical analysis.

EXAMPLE 4 1 -[(Di-2-chloroethoxyphosphonyl)methyl]-2,4- and2,6-diaminobenzenes, 1b

Recrystallized product of Example 3 (2.27 g, 58.6 nmol) was dissolved in40 ml of absolute ethanol and a small amount of catalyst, 10% palladiumon carbon, was added. The hydrogenation was carried out as in Example 2.A solid product was obtained (1.88 g, 98%, mp 105°-109° C.).Recrystallizations from benzene gave an analytical sample: mp 116°-119°C. Structure was confirmed ¹ H-NMR and chemical analysis.

EXAMPLE 5 Bismaleimide, 2a

To a vigoursly stirred solution of 1a (7.37 g, 28.5 mmol) in acetoneunder nitrogen atomsphere, granular maleic anhydride (6.16 g, 62.8 mmol)was added portionwise so that the temperature was maintained at about40° C. After stirring at room temperature for about 30 min. thebismaleamic acid was precipitated as a pale yellow solid. Stirring wascontinued for 1.5 hr. more to complete the reaction. Cyclodehydration ofbismaleamic acid to bismaleimide was carried out by adding aceticanhydride and fused sodium acetate (300 ml and 27 g respectively permole of maleic anhydride) to the reaction mixture and refluxing for 2hr. The suspension became a brown solution during the first 15 min. ofrefluxing. Most of the acetone was evaporated at the end of thereaction. The mixture was poured into ice water and extracted bychloroform. The layer of chloroform was subsequently washed by a 5%aqueous solution of NaHCO₃, followed by water and then dried, (MgSO₄).The concentrate obtained after removing of volatile components using arotary evaporator was dried in a vacuum oven at about 50° C. overnight.Bismaleimide 2a was obtained as a brown solid (10.96 g, 92%) andpurified from tetrahydrofuran/ether.

EXAMPLE 6 Bismaleimide, 2b

A mixture of diamine 1b (4.01 g, 12.3 mmol) and maleic anhydride (2.64g, 27.0 mmol) reacted as described in Example 5. The yield of thereaction was 94% (5.63 g).

EXAMPLE 7 Biscitraconimide, 3a

Biscitraconimide 3a was prepared by reacting diamine 1a (4.34 g, 16.8mmol) with citraconic anhydride (4.14 g, 37.0 mmol) as in Example 5. Theyield of the reaction was 91% (6.82 g).

EXAMPLE 8 Biscitraconimide, 3b

A mixture of diamine 1b (3.90 g, 11.9 mmol) and citraconic anhydride(2.94 g. 26.2 mmol) reacted as in Example 5. Biscitraconimide 3b wasobtained with a yield 93% (5.70 g).

EXAMPLE 9 Bismaleimide, 4a

Maleic anhydride (1.62 g, 16.6 mmol) was added portionwise to a stirredsolution of diamine 1a (3.89 g, 15.1 mmol) in acetone under nitrogenatmosphere. After stirring for 2 hr,3,3',4,4'-benzophenonetetracarboxylic dianhydride (2.43 g, 7.5 mmol) wasadded to the solution and stirring was continued at ambient temperaturefor 2 hr longer. To the continuously stirred solution of polyamidecarboxylic acid, acetic anhydride and fused sodium acetate (300 ml and27 g respectively per mole of water condensed) were added and acetonewas allowed to reflux for 2-3 hr. The reaction mixture was poured intoice water, extracted with chloroform and the layer of chloroform waswashed with a 5% aqueous solution of NaHCO₃ subsequently with water anddried with MgSO₄. Upon concentration in a rotary evaporator,bismaleimide 4a was obtained as a brown solid (5.41 g, 75%) and purifiedfrom tetrahydrofuran/ether.

EXAMPLE 10 Bismaleimide, 4b

Diamine 1b (2.01 g, 6.2 mmol) and maleic anhydride (0.66 g, 6.8 mmol)were dissolved in acetone and the solution was stirred under nitrogenatmosphere for 2 hr. 3,3',4,4'-Benzophenone tetracarboxylic dianhydride(0.99 g, 3.1 mmol) was added to the solution and stirring was continuedfor 2 hr more. Cyclodehydration and isolation of the bismaleimide 4b wascarried out as in Example 9. The yield of the reaction was 72% (2.46 g).

EXAMPLE 11 Bismaleimide, 5a

Diamine 1a (8.27 g, 32.0 mmol) reacted with maleic anhydride (3.45 g,35.2 mmol) according to the procedure described in Example 5 to yieldthe mono-N-maleimido derivative of 1a.

Methylenebis(4-phenylisocyanate) (4.00 g, 16.0 mmol) dissolved inacetone was rapidly added to a vigorously stirred solution ofmono-N-maleimido derivative of 1a in acetone under nitrogen atomsphere.After subsiding, the exothermic reaction the mixture was heated to50°-60° C. for 1 hr. Bismaleimide 5a (12.16 g, 82%) was precipitated byadding ether to the reaction mixture and purified from acetone/ether.

EXAMPLE 12 Bismaleimide, 5b

The mono-N-maleimido derivative of 1b was prepared by reacting diamine1b (4.25 g, 13.0 mmol) with maleic anhydride (1.40 g, 14.3 mmol) as inExample 5.

To a vigorously stirred solution of the mono-N-maleimido derivative of1b in acetone, methylenebis(4-phenylisocyanate) (1.62 g, 6.5 mmol) wasrapidly added under nitrogen atmosphere. After the exothermic reactionsubsided, the mixture was heated to 50°-60° C. for 1 hr. Bismaleimide 5b(5.95 g, 86%) was precipitated by adding ether to the reaction mixtureand purified from acetone/ether.

                  TABLE 1                                                         ______________________________________                                        Characteristic DSC Temperatures of Bisimides                                  Compound  T.sub.1 (°C.)                                                                       T.sub.2 (°C.)                                                                   T.sub.3 (°C.)                          ______________________________________                                        2a        200          233      282                                           2b        180          224      260                                           6         205          249      326                                           3a        178          240      288                                           3b        168          236      256                                           4a        216          241      292                                           4b        180          210      248                                           5a        140          275      300                                           5b        130          259      320                                           ______________________________________                                    

                                      TABLE 2                                     __________________________________________________________________________    Thermal Stability of Polymers                                                 In Nitrogen                   In Air                                                                  Char Yield               Char Yield                   Polymer                                                                            PDT (°C.)                                                                    PDT.sub.max (°C.)                                                             TCP (°C.)                                                                    700° C., %                                                                   PDT (°C.)                                                                    PDT.sub.max (°C.)                                                             TCP (°C.)                                                                    700° C.,              __________________________________________________________________________                                                     %                            2'a  386   433    495   66    378   433    455   62                           2'b  314   428    478   63    292   365    450   57                           6'   457   508    560   51    445   497    536    4                           3'a  408   456    500   69    400   452    495   65                           3'b  393   447    485   70    379   436    480   58                           4'a  388   474    520   68    375   460    495   56                           4'b  309   466    490   61    300   390    483   51                           5'a  334   369    512   63    325   353    487   46                           5'b  331   394    490   58    329   384    468   35                           __________________________________________________________________________

                  TABLE 3                                                         ______________________________________                                        Limiting Oxygen Index and                                                     Smoke Density of Some Polymers*                                               Polymer  Phosphorus (%)                                                                              LOI    Smoke Density                                   ______________________________________                                        2'a      7.51          48.3   4.4                                             2'b      6.30          71.6   1.1                                             6'       0             41.0   34.0                                            ______________________________________                                         *At a heat flux of 3.3 w/cm.sup.2 and for an irradiation time of 5 min.  

While the present invention has been described with reference tospecific embodiments thereof, it will be understood by those skilled inthis art that various changes may be made and that equivalent steps maybe substituted without departing from the true spirit and scope of thepresent invention. All such modifications or changes are intended to beincluded within the scope of the following claims.

We claim:
 1. 1-[(Diorganooxyphosphonyl)methyl]benzene bismaleimide ofthe formula: ##STR15## wherein: R is an organo group selected fromalkyls, halogenated alkyls and aryls;R¹ is hydrogen or lower alkyl; andthe maleimido groups are in the 2,4 or 2,6 positions.
 2. Thebismaleimide of claim 1 wherein said maleimido groups are predominantlyin the 2 and 4 positions.
 3. The bismaleimide of claim 2 wherein R¹ ishydrogen.
 4. The bismaleimide of claim 2 wherein R¹ is alkyl.
 5. Thebismaleimide of claim 4 wherein R¹ is methyl.
 6. The bismaleimide ofclaim 3 wherein R is alkyl.
 7. The bismaleimide of claim 6 wherein R isethyl.
 8. The bismaleimide of claim 3 wherein R is halogenated alkyls.9. The bismaleimide of claim 8 wherein R is 2-chloroethyl.
 10. Thebismaleimide of claim 4 wherein R is substituted alkyl.
 11. Thebismaleimide of claim 10 wherein R is 2-chloroethyl.
 12. A method ofproducing a [(diorganooxyphosphonyl)methyl]benzene bismaleimide of theformula: ##STR16## wherein: R is an organo group selected from alkyls,aryls and halogenated alkyls;R¹ is hydrogen or lower alkyl, and thebismaleimide groups are in the 2,4 or 2,6-positions, which methodcomprises:(a) reacting one equivalent of a diamino compound of theformula: ##STR17## wherein R is defined hereinabove; with two or moreequivalents of an anhydride of the formula: ##STR18## wherein R¹ is asdefined hereinabove; and (b) recovering said bismaleimide.
 13. Themethod of claim 12 wherein said bismaleimide groups are predominantly inthe 2 and 4 positions.
 14. The method of claim 13 wherein R is alkyl.15. The method of claim 14 wherein R is ethyl.
 16. The method of claim13 wherein R is halogenated alkyl.
 17. The method of claim 16 wherein Ris 2-chloroethyl.
 18. The method of claim 13 wherein R¹ is lower alkyl.19. The method of claim 18 wherein R¹ is methyl. 20.1-[(Diorganooxyphosphonyl)methyl] benzene bismaleimide of the formula:##STR19## wherein: R is an organo group selected from alkyls having from1 to 10 carbon atoms, halogenated alkyls and aryls;R¹ is hydrogen orlower alkyl; and the maleimido groups are in the 2,4 or 2,6 positions.21. The bismaleimide of claim 20 wherein said maleimido groups arepredominantly in the 2 and 4 positions.
 22. The bismaleimide of claim 21wherein R¹ is hydrogen.
 23. The bismaleimide of claim 21 wherein R¹ isalkyl.
 24. The bismaleimide of claim 23 wherein R¹ is methyl.
 25. Thebismaleimide of claim 22 wherein R is alkyl.
 26. The bismaleimide ofclaim 25 wherein R is ethyl.
 27. The bismaleimide of claim 22 wherein Ris halogenated alkyl.
 28. The bismaleimide of claim 27 wherein R is2-chloroethyl.
 29. The bismaleimide of claim 23 wherein R is halogenatedalkyl.
 30. The bismaleimide of claim 29 wherein R is 2-chloroethyl. 31.A method of producing a [(diorganooxyphosphonyl)methyl]benzenebismaleimide of the formula: ##STR20## wherein: R is an organo groupselected from alkyls having from 1 to 10 carbon atoms, halogenatedalkyls and aryls;R¹ is hydrogen or lower alkyl, and the bismaleimidegroups are in the 2,4 or 2,6-positions, which method comprises:(a)reacting one equivalent of a diamino compound of the formula: ##STR21##wherein R is defined hereinabove; with two or more equivalents of ananhydride of the formula: ##STR22## wherein R¹ is as definedhereinabove; and (b) recovering said bismaleimide.
 32. The method ofclaim 31 wherein said bismaleimide groups are predominantly in the 2 and4 positions.
 33. The method of claim 32 wherein R is alkyl.
 34. Themethod of claim 33 wherein R is ethyl.
 35. The method of claim 32wherein R is halogenated alkyls.
 36. The method of claim 35 wherein R is2-chloroethyl.
 37. The method of claim 32 wherein R¹ is lower alkyl. 38.The method of claim 37 wherein R¹ is methyl.